Classification of Elements and Periodicity in Properties

Classification of Elements and Periodicity in Properties

Question

Which of the following atoms has the highest first ionisation energy?

  • Na

  • K

  • Sc

  • Rb

Answer

C.

Sc

Order of first ionisation energy is Sc> Na > K > Rb. Due to poor shielding effect, removal of one electron from 4s orbital is difficult as compared to 3s-orbital.

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